The present invention relates to an electronic watermark embedding device and an electronic watermark detecting device, and an electronic watermark embedding method and an electronic watermark detecting method implemented therein. More particularly, the present invention is concerned with a technology of embedding an electronic watermark in an enlarged or reduced image or video and a technology of detecting an embedded electronic watermark.
In recent years, electronic-media data including image or video data and multimedia data has spread rapidly along with an advance in technologies. For simplifying identification of a source of electronic-media data, an electronic watermark is often embedded in an image or video. Specifically, a provider of electronic-media data embeds the electronic watermark in electronic-media data to be provided. The provider can be specified with the electronic watermark. The embedded electronic watermark is detected using software or hardware, whereby the provider proves to own the copyright on the electronic-media data. Copyrights are thus managed and put into effect.
The foregoing electronic watermark embedding method or detecting method has been disclosed in, for example, Japanese Unexamined Patent Publication (JP-A) No. 10-145757 or JP-A No. 10-191330.
According to the foregoing electronic watermark embedding method, the electronic watermark is embedded in the image or video in units of a block. Therefore, after the electronic watermark is embedded, if the image or video is enlarged or reduced, the embedded electronic watermark may not be detected any longer.
Talking of an example of enlargement or reduction of the image or video, the image or video may be reduced and transmitted when, for example, a telecommunication line such as radio broadcasting permits only a low transmission rate. In this case, after the electronic watermark is embedded, the image or video is reduced. It is therefore hard to detect the electronic watermark in the image or video broadcast through radio broadcasting.
Moreover, if the image or video is enlarged or reduced by a so-called pirate, the electronic watermark cannot be detected. There is an increasing demand for an electronic watermark embedding device and an electronic watermark detecting device that can cope with enlargement or reduction.